Photographic silver-bleaching composition

ABSTRACT

A COMPOSITION FOR BLEACHING PHOTOGRAPHIC SILVER WHICH IS RAPID ACTING AND SUITABLE FOR USE IN EITHER COLOR OR BLACK-AND-WHITE PROCESSING COMPRISES A DILUTE AQUEOUS SOLUTION OF (1) A PERSULFATE SALT OR A NITROSODISULFONATE SALT AND (2) AN AROMATIC AMINE TYPICALLY OF THE FORMULA:   1-(X-N(-Y)-),2-R1,3-R2,4-R3,5-R4,6-R5-BENZENE   WHERE X AND Y ARE HYDROGEN OR LOWER ALKYL AND R1, R2, R3, R4 AND R5 ARE HYDROGEN, AMINO, HYDROXYL, LOWER ALKYL, LOWER MONOALKYLAMINO OR LOWER DIALKYLAMINO EXCEPT THAT AT LEAST ONE OF R1 TO R5 IS A SUBSTITUENT OTHER THAN HYDROGEN.

United States Patent Ofice 3,707,374 Patented Dec. 26, 1972 3,707,374 PHOTOGRAPHIC SILVER-BLEACHING COMPOSITION Carol R. Van Der Voorn and Roland G. Willis, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y. No Drawing. Filed Aug. 17, 1970, Ser. No. 64,625 Int. Cl. G03c /32, 7/16 US. Cl. 96-60 16 Claims ABSTRACT OF THE DISCLOSURE A composition for bleaching photographic silver which is rapid acting and suitable for use in either color or black-and-white processing comprises a dilute aqueous solution of (1) a persulfate salt or a nitrosodisulfonate salt and (2) an aromatic amine typically of the formula:

where X and Y are hydrogen or lower alkyl and R R R R and R are hydrogen, amino, hydroxyl, lower alkyl, lower monoalkylamino or lower dialkylamino except that at least one of R to R is a substituent Other than hydrogen.

This invention relates in general to the art of photographic processing and in particular to the bleaching of photographic silver. More specifically, this invention relates to a novel silver bleach solution and to the process of bleaching silver in a photographic emulsion layer by contacting the photographic element with the bleach solution.

In the processing of photographic silver halide color elements and in some black-and-white photographic processes, it is necessary to remove metallic silver formed during development. This is ordinarily accomplished by the use of a silver bleaching composition which converts metallic silver into a soluble silver salt. The most commonly used bleach for this purpose is an aqueous solution of a water-soluble ferricyanide, such as sodium or potassium ferricyanide, and an alkali metal bromide. While satisfactory results are generally obtained by the use of ferricyanide bleach baths, problems of stain formation are encountered in some color processes as a result of oxidation of organic molecules by the ferricyanide leading to colored products which are not readily removed. Furthermore, use of ferricyanide bleach baths in large scale processing installations gives rise to serious problems of water pollution. For example, the ferricyanide ions which are present in the waste bleach solution which is discharged from such processes will undergo gradual oxidation to form cyanide ions, and these are among the most toxic to fish and other aquatic life of any of the wastes discharged from photographic processing. There is, accordingly, a need for new photographic silver bleach compositions which are eifective in accomplishing the removal of silver from photographic elements without the disadvantages of stain formation or water pollution, and it is toward this end that the present invention is directed.

The novel photographic silver bleach composition of this invention comprises an aqueous solution of 1) a water-soluble persulfate salt or a water-soluble nitrosodisulfonate salt and (2) an aromatic amine. While persulfate salts and nitrosodisulfonate salts are not in themselves sufiiciently active silver oxidizing agents to serve as a useful bleach in photographic processing, it has been found that when they are used together with small amounts of aromatic amines, as hereinafter described in detail, the resulting solution is an effective rapid-acting silver bleach. Other agents commonly employed in photographic bleach compositions, such as alkali metal bromides, alkali metal chlorides, ammonium bromide or ammonium chloride to aid bleaching, and buffers to control pH, are also incorporated in the bleach solution of this invention, if desired.

Bleach compositions prepared in accordance with the present invention are useful for bleaching photographic silver in black-and-white photographic elements. They are also useful in bleaching photographic silver in a color photographic element and provide the important advantage that they bleach the silver without detrimentally affecting image dyes, or otherwise causing stains in the emulsion layer. A further important feature of the novel bleach compositions described herein is that the exhausted bleach solution is substantially innocuous and may be disposed of without contributing significantly to water pollution. The persulfate salts and nitrosodisulfonate salts utilized in the bleach composition of this invention are water-soluble compounds typically of the formulas:

M 5 0 and [M] (SO NO], respectively where M represents ammonium or an alkali metal such as sodium, potassium or lithium. These are well known compounds. The use of nitrosodisulfonate salts as intensifiers of the latent photographic image is described in U.S. Pat. 2,938,793, but they have not heretofore been employed in silver bleach baths. Alkali metal persulfates have been used in silver image reducing baths to lower image density; however, these compounds bleach silver too slowly to be useful for removal of silver in commercial photographic processing. Alkali metal persulfates are used to oxidize alkali metal ferrocyanide to alkali metal ferricyanide in spent ferricyanide bleach baths used in color photographic processing as described in West et al., US. Pat. 2,944,895. Alkali metal ferricyanide is the silver bleaching agent in the bleach solutions of the West et a1. patent.

The aromatic amines which are of particular utility for the purposes of this invention are water-soluble nuclear (i.e., ring) substituted aromatic amines of the formula:

wherein X and Y are independently selected from the group consisting of hydrogen and lower alkyl and R R R R and R are independently selected from the group consisting of hydrogen, amino (i.e., -NH hydroxyl, lower alkyl, lower monoalkylamino and lower dialkylamino, with the proviso that at least one of R R R R and R is a substituent other than hydrogen. As employed herein, the term lower alkyl is intended to mean an alkyl radical of 1 to 4 carbon atoms, e.g., methyl, ethyl, n-propyl, isopropyl, isobutyl, t-butyl or n-butyl. Illustrative examples of aromatic amines of the above formula include the following:

p-phenylenediamine p-aminophenol p-toluidine p-methylaminophenol p-dimethylaminophenol N-methyl-p-phenylenediamine 'N,N-dimethyl-p-phenylenediamine N,N,N-trimethyl-p-phenylenediamine N,N,N',N'-tetramethyl-p-phenylenediamine 2-methyl4-diethylamino-aniline 2-methyl-4-methylamino-aniline 4-dimethylamino-N-methylaniline m-phenylenediamine o-phenylenediamine 2,3,5,6-tetramethyl-pphenylenediamine 2,4-diaminophenol and the like.

The photographic silver bleach compositions of this invention are dilute aqueous solutions of an aromatic amine and a persulfate salt or a nitrosodisulfonate salt, as described hereinabove, in which the persulfate salt or the nitrosodisulfonate salt is utilized in substantially greater concentration than the aromatic amine and in which the two agents function synergistically to provide a rapidacting silver bleach. More specifically, the bleach compositions of this invention comprise an aqueous solution of at least about 0.02 gram of the aromatic amine per liter of solution and at least about five parts of persulfate salt or the nitrosodisulfonate salt per part by weight of the aromatic amine. The persulfate salt or the nitrosodisulfonate salt is advantageously utilized in any desired amount which is greater than the aforesaid minimum, up to the limit of its solubility in the solution. Preferred compositions are comprised of about 0.02 to about 2 grams of the aromatic amine per liter of solution and at least about five parts of the persulfate salt or the nitrosodisulfonate salt per part by weight of the aromatic amine, while particularly preferred compositions are comprised of about 0.05 to about 1 gram of the aromatic amine per liter of solution and at least about ten parts of the persulfate salt or the nitrosodisulfonate salt per part by weight of the aromatic amine.

In addition to (1) the persulfate salt or the nitrosodisulfonate salt and (2) the aromatic amine, other addenda commonly utilized in photographic silver bleach compositions can be incorporated in the bleach baths of this invention. For example, the bleach bath advantageously contains an alkali metal halide or ammonium halide such as sodium bromide, potassium bromide, ammonium bromide, sodium chloride, potassium chloride, ammonium chloride which function to aid in the bleaching. It is advantageous to also incorporate a butter in the bleach bath to provide proper pH control. For this purpose, any of the buffers commonly used in photographic processing solutions may be employed, e.g., phosphoric acid, alkali metal phosphates, acetic acid, alkali metal acetates, maleic acid, alkali metal maleates, alkali metal borates, etc. Preferably, the bleach bath will be buffered to a pH in the range from about 1.9 to about 9, while optimum results are ordinarily obtained with a pH of about 6.

While applicants do not intend to be bound by any theoretical explanation for the manner in which their invention functions, it is believed that when an aqueous solution of -(l) the persulfate salt of the nitrosodisulfonate salt and (2) the aromatic amine is prepared, a chemical reaction between these two agents occurs to form a quinoneimine and that the quinoneimine functions catalytically to greatly accelerate the rate at which the solution bleaches silver. Thus, for example, it has been reported in the literature that p-toluidine reacts with potassium nitrosodisulfonate to form 2-amino-5-methyl-N-(ptolyl)-p-benzoquinoneimine. See Chem. Ber. 87, 1841 (1954). The persulfate or nitrosodisulfonate salts are not sufiiciently active silver oxidizing agents to be used by themselves in a photographic bleach bath and the aromatic amines do not function as silver bleaching agents. How- 4 ever, in solutions prepared in accordance with the teachings provided herein, the persulfate salt or the nitrosodisulfonate salt is used in substantially greater concentration than the aromatic amine and the excess persulfate salt or nitrosodisulfonate is apparently catalyzed by the quinoneimine which is formed to thereby provide a rapidacting silver bleach.

The invention is further illustrated by the following examples of its practices:

EXAMPLE 1 Four silver-bleachingcompositions .within the scope of the present invention are prepared by dissolving potassium nitrosodisulfonate, potassium bromide and N,N,N', N-tetramethyl-p-phenylene-diamine in pH 6.0 phosphate buffer (ionic strength=0.375 in the proportions described hereinbelow. To evaluate the effectiveness of these solutions as silver bleaches, 35-min. strips of black-and-white film comprising a gelatin silver halide emulsion coated at 350 mg./ft. silver on a cellulose acetate film support, designated hereinafter as film A, are exposed to room light, fully developed at room temperature (i.e., 20 C.) in a developer solution containing monomethyl-p-aminophenolsulfonate and ascorbic acid and having a pH of 10.0, stopped, washed, and then treated with the bleach solution. The compositions of the bleach solutions and the bleaching time required to reduce the silver density from 3.90 to 0.05 are reported in Table I.

In contrast with the above tabulated results, the bleaching time for the same film processed in the same manner,

except that the N,N,N,N tetramethyl-p-phenylenediamine is omitted from the bleaching solution, is 37 minutes.

EMMPLE 2 Samples ofthree different color films of the incorpo rated-coupler type are exposed to room light, fully developed, stopped by immersion in a 3% solution of acetic acid, washed, and then treated with bleach solution number 4 of Example 1. The color films, designated hereinafter by the letters B, C and D, are single-layer coatings on a cellulose acetate film support of a coarse-grain brornoiodide gelatin emulsion containing mg./ft. silver and the couplers utilized are l-hydroxy-N-[ot-(2,4-di-t-amylphenoxy)-butyl]-2-naphthamide in film B, 1-(2,4,6-trichlorophenyl)-3-{3-[ct-(2,4 di t amylphenoxy)acetamido]benzarnido}-5-pyrazolone in film C, and u-{3-[oi- (2,4-di-t-amyl phenoxy)butyramideJbenzoyl} 2 methoxyacetanilide in film D. The developing bath is prepared by adding two grams of sodium sulfite, one gram of potassium bromide and four grams of 2-amino-5-diethylaminotoluene hydrochloride to one liter of-0.l25 and N potassium phosphate solution having a pH of 12 and a temperature of 20 C. The bleaching time required to reduce the silver density from 0.55 to zero is 2 minutes for film B, 5 minutes for film C, and 3.5 minutes for film D. In each case, the bleaching bath has no adverse affect on the dye generated during the color development step.

EXAMPLE 3 Eleven different silver-bleaching baths within the scope of the present invention are prepared by dissolvinglO grams of potassium nitrosodisulfonate, 10 grams of potassiumbromide, and 0.25 gram of an aromatic amine, as hereinafter described, in one liter of pH 6.0 phosphate buffer (ionic strength=0.375). Samples of the black-andwhite film of Example 1 and the three color films of Example 2 are processed in the same manner as described in these examples and then treated with each of the aforesaid bleach baths (except in those instances where no data are reported) for a period of time sufiicient to effect the same change in silver density as described in Examples 1 and 2. The aromatic amines utilized and the bleaching times obtained are reported in Table II.

TABLE II Bleaching time (minutes) Bleach Film Film Film Film solution Aromatic amine A B C D 5 p-Phenylenediamine 9.75 1.4 2.25 2 6 Z-methyl-l-methylamino- 7 1.25 2 2.5

aniline. 7 2-methyl-4-diethylamino- 4.9 1.3 1.25

aniline. 8 4-dimethylamino-N-methyl- 8 1.5 1 5 l 5 aniline.

.5 .4 .7 .5 .0 2,3,5,6-tetramethyl-p- .0

phenylenedi amine 15 2,4-diaminophenol In comparison with the results in Table II, when samples of the same films are bleached in a ferricyanide bleach bath, consisting of 10 grams potassium ferricyanide and 10 grams potassium bromide in one liter of a potassium phosphate buifered aqueous solution, the bleaching times for films A, B, C and D are 5.4 minutes, 1.4 minutes, 1.5 minutes, and 1.5 minutes, respectively.

EXAMPLE 4 A bleach bath is prepared by dissolving 10 grams of potassium nitrosodisulfonate, 10 grams of potassium bromide, and 0.25 gram of p-toluidine in one liter of 5% aqueous acetic acid and bufi'ering to a pH of 4.43 by addition of sodium hydroxide. An exposed and developed color photographic element, similar to those described in Example 2, with a silver density of 0.55 is treated in this bath and bleached to a density of 0.18 in one minute and to a density of 0.04 in two minutes. Using the same bath, but omitting the potassium nitrosodisulfonate, has no effect on the silver density, i.e., the bath has no bleaching action whatever. Using the same bath, except that the ptoluidine is omitted, a sample of the same film is bleached to a density of 0.38 in one minute and to a density of 0.27 in two minutes.

EXAMPLE 6 Nine 35-min. strips of black-and-white film described in Example 1 are exposed and processed as described in Example 1, except that bleach solutions A, B, C, D, E, F, G, H and I are used. These bleach solutions are made by adding 100 mg. of the indicated aromatic amine identified in Table III to separate 100 ml. aliquot portions of a 1 liter aqueous solution (pH 1.9) containing 100 g. ammonium chloride, and 100 g. of ammonium persulfate. Solution A, containing no aromatic amine, is used as a control. The bleach time required to reduce the silver density from 3.90 to 0.95 are reported in Table III.

TABLE III Bleach Bleach time in solution Aromatic amine minutes A None 30-40 p-Toluidine 4.5 p-Phenylenediamine D N-methyl-p-phenylenediamine N ,N-dimethyl-p-phenylenediamine N ,N ,N-trimethyl-p-phenylenediamine N,N,N,N-tetramethyl-p-phenylenediam no p-Ammophenol I p-Methylaminophenol The results illustrate the valuable bleach compositions of our invention which contain ammonium persulfate as the bleaching agent in combination with various aromatic amines. The control containing ammonium persnlfate and no aromatic amine is so slow that it would not be useful in commercial photographic processing operations.

EXAMPLE 7 The procedure described in Example 6 is repeated with portions of the bleach solution containing the aromatic amine N,N,N,N' tetramethyl p phenylenediamine (TMPD) at the concentrations indicated in Table IV where the bleach times are reported.

TABLE IV Concentration of TMPD Bleach time in mg./ 1.: in minutes 0 30-40 50 9 EXAMPLE 8 Similar results are obtained when Example 9 is repeated with bleach solution when pHs are adjusted by an acetate buffer, a borate buffer and a phosphate bulfer to pHs in the range of from about 1.9 to about 9.0.

EXAMPLE 9 The procedure described in Example 2 is repeated with a bleach solution of Example 7 containing 1 g. of TMPD per liter. The bleaching time required to reduce the silver density from 0.55 to zero is 60 seconds for film B, 50 seconds for film C and 35 seconds for film D. In each instance, the bleaching bath has no adverse effect on the dye generated during the color development step.

Itis apparent from consideration of the above examples, that an effective rapid-acting silver-bleaching composition is obtained by use of (1) either a persulfate salt or a nitrosodisulfonate salt, together with (2) an aromatic amine. While the persulfate salt or the nitrosodisulfonate salt by itself is a poor silver bleach, each of these salts, combined with an aromatic amine, together function synergistically to provide a bleach which acts at a rate comparable to that of the ferricyanide bleaches of the prior art. Bleaches prepared from the combination of (l) a persulfate salt or a nitro'sodisulfonate salt and (2) arematic amine have also been found to rapidly bleach photographic silver without adversely affecting the image dyes present in color elements. Furthermore, the used bleach solution is readily disposed of without presenting the pollution hazard encountered with the ferricyanide bleaches.

The invention has been described in deail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

We claim:

1. A photographic silver-bleaching composition consisting essentially of a dilute aqueous solution of (1) a salt selected from the class consisting of a persulfate and a nitrosodisulfonate salt and (2) an aromatic amine of the formula:

wherein X and Y are independently selected from the group consisting of hydrogen and lower alkyl and R R R R and R are independently selected from the group consisting of hydrogen, amino, hydroxyl, lower alkyl, lower monoalkylamino and lower dialkylamino with the proviso that at least one of R R R R and R is a substituent other than hydrogen; said aqueous solution being a solution of at least about 0.02 gram of said aromatic amine per liter of solution and at least about 5 parts of said nitrosodisulfonate salt per part by weight of said aromatic amine.

2. A photographic silver-bleaching composition as described in claim 1, wherein said aqueous solution is a solution of from about 0.02 to about 2 grams of said aromatic amine per liter of solution and at least about 5 parts of said salt selected from the class consisting of said persulfate salt and said nitrosodisulfonate salt per part by weight of said aromatic amine.

3. A photographic silver-bleaching composition as described in claim 1, wherein said aqueous solution is a solution from about 0.5 to about 1 gram of said aromatic amine per liter of solution and at least about parts of said salt selected from the class consisting of said persulfate salt and said nitrosodisulfonate salt per part by weight of said aromatic amine.

4. A photographic silver-bleaching composition as described in claim 1, wherein said composition is buifered to a pH in the range from about 1.9 to about 9.

5. A photographic silver-bleaching composition as described in claim 1, wherein said composition is buttered to a pH of about 6.

6. A photographic silver-bleaching composition as described in claim 1 additionally comprising an alkali metal bromide.

7. A photographic silver-bleaching composition as described in claim 3, wherein said nitrosodi'sulfonate salt is potassium nitrosodisulfonate and said aromatic amine is selected from the group consisting of p-phenylenediamine, p-aminophenol, p-toluidine, p-methylaminophenol, p-dimethylaminophenol, N,N,N,N'-tetramethyl-p-phenylenediamine, 2 methyl 4 diethylaminoaniline, 2-methyl-4- methylamino-aniline, 4 dimethylamino-N-methylaniline, m-phenylenediamine, o-phenylenediamine, 2,3,5,6-tetramethyl-p-phenylenediamine and 2,4-diaminophenol.

8. A photographic silver-bleaching composition as described in claim 3, wherein said persulfate salt is ammonium persulfate and said aromatic amine is selected from the class consisting of p-aminophenol, p-toluidine, pmethylaminophenol, p-phenylenediamine, N-methyl-pphenylenediamine, N,N-dimethyl-p-phenylenediamine, N, N,N-trimethyl-p-phenylenediamine and N,N,N',N'-tetramethyl-p-phenylenediamine.

9. A method of bleaching silver in an emulsion layer of an exposed photographic element after development thereof which comprises contacting said exposed and developed element with a silver-bleaching composition consisting essentially of a dilute aqueous solution of 1) a salt selected from the class consisting of a persulfate salt and a nitrosodisulfonate salt and (2) an aromatic amine of the formula:

wherein X. and Y are independently selected from the group consisting of hydrogen and lower alkyl and R R R R and R are independently selected from the group consisting of hydrogen, amino, hydroxyl, lower alkyl, lower monoalkylamino and lower dialkylamino with the proviso that at least one of R R R R and R is a substituent other than hydrogen; said aqueous solution being a solution of at least about 0.02 gram of said aromatic amine per liter of solution and at least about 5 parts of said nitro'sodisulfonate salt per part by weight of said aromatic amine.

10. A method as described in claim 9, wherein said aqueous solution is a solution of from about 0.02 to about 2 grams of said aromatic amine per liter of solution and at least about 5 parts of said salt selected from the class consisting of said persulfate salt and said nitrosodisulfonate salt per part by weight of said aromatic amine.

11. A method as described in claim 9, wherein said aqueous solution is a solution of from about 0.05 to about 1 gram of said aromatic amine per liter of solution and at least about 10 parts of said salt selected from the class consisting of said persulfate salt and said nitrosodisulfonate salt per part by weight of said aromatic amine.

12. A method as described in claim 9, wherein said composition is bufiered to a pH in the range from about 1.9 to about 9.

13. A method as described in claim 9, wherein said composition is buffered to a pH of about 6.

14. A method as described in claim 9, wherein said composition additionally comprises an alkali metal bromide.

15. A method as described in claim 11, wherein said nitrosodisulfonate salt is potassium nitrosodisulfonate and said aromatic amine is selected from the group consisting of p-phenylenediamine, p-aminophenol, p-toluidine, pmethylaminophenol, p-dimethylaminophenol, N,N,N',N'- tetramethyl p phenylenediamine, 2-methyl-4-diethylamino-aniline, Z-methyl-4-methylamino-aniline, 4-dimethylamino-N-methylaniline, m-phenylenediamine, o-phenylenediamine, 2,3,5,6-tetrarnethyl-p-phenylenediamine and 2,4-diaminophenol.

16. A method as described in claim 11, wherein said persulfate salt is ammonium persulfate and said aromatic amine is selected from the class consisting of p-aminophenol, p-toluidine, p-methylaminophenol, p-phenylenediamine, N-methyl-p-phenylenediamine, N,N-dimethyl-pphenylenediamine, N,N,N-trimethyl-p-phenylenediamine and N,N,N',N'-tetramethyl-p-phenylenediamine.

References Cited UNITED STATES PATENTS 2,625,477 I/ 1953 Sawdey 96-60 2,705,201 3/ 1955 Tulagin 9660 2,938,793 5/ 1960 Goldberg et al 9665 3,042,520 7/ 1962 Johnson 9622 FOREIGN PATENTS 1,133,500 11/1968 Great Britain 9622 DAVID KLEIN, Primary Examiner M. F. KELLEY, Assistant Examiner US. Cl. X.R. 9622 

